The Sun reported that Ms Lee wrote on the forum on September 4 that she was "desperate" and wanted to "do it ASAP". She wrote: "I haven’t the strength to do this alone. I’m not a cop, a cannibal or a murderer, just desperate. I have all the ingredients and want to do it ASAP."

The bodies were found in the fume-filled car, which had notes placed on the windows warning of the toxic chemicals inside. The Sun said Ms Lee, who reportedly had a severe eating disorder, had used the forum to ask advice on concocting a toxic mix to take her own life.

A source close to the investigation said: "We believe they met a few hours before this tragedy."

The bodies were found on Monday morning by a warehouse worker but sources said it is possible the car had been parked on the site over the weekend, when the area is largely deserted. Essex Police said the deaths, near Braintree Enterprise Centre, were "highly unusual" and confirmed that "noxious" substances had been found inside the vehicle. The force is treating the deaths as unexplained.

Essex County Fire and Rescue Service said it is thought the chemical involved was hydrogen sulphide, a highly poisonous gas. Firefighters had to wear gas-tight suits to remove the bodies from the car.

Mr Lumb’s father Melvyn, who shared a home with him, said he was too upset to pay tribute to his son on Tuesday. He said of the tragedy: "It’s just a shock."